Although the first useful lasers were developed in the 1960s, recent advances in laser and fiber optic delivery systems have greatly enhanced the use of this technology in the field of medicine. Today there are numerous types of laser systems designed for operation in a wide range of applications primarily related to surgical and other medical procedures.
A common type of laser known as a CO2 laser delivers radiation with a wavelength of 10.64 microns. However, in order to focus or channel the radiated energy produced by a CO2 laser it is necessary to configure sets of mirrors in certain ways. These systems are typically large and expensive. With the advent of the Nd:YAG type laser delivering electromagnetic energy at a wavelength of 1.064 microns, it became possible to generate and focus the laser radiation through a silica core optical fiber. Thus, fiber optic surgical tools have become important in certain procedures. The range of their utility is still being explored and discovered.
Laser fibers are used in different ways, including incision, necrosis or killing of live tissue, excision or removal of tissue and structure, and cauterization of tissue. A very focused beam would provide the greatest amount of control during either operation. Cauterization and necrosis of living tissue is accomplished by coagulation, or more precisely with respect to the laser itself, by photocoagulation of contacted or penetrated tissue. In this process the laser beam causes the proteins in the contacted tissue to heat up rapidly and thermally denature. This essentially kills living tissue and seals blood vessels. The process has been likened to frying an egg. In practice, during an incision procedure cauterization of the incised tissue is likely to occur simultaneously. Thus, laser surgery is often characterized by an absence of bleeding during the surgery.
In the prior art there are described devices which generate a dual wavelength beam of radiation and effect both cutting and cauterizing simultaneously. Such devices generally use one type of laser with some type of harmonic generator for providing half or double fundamental wavelength beams. There also exist inventions which deliver energy at much shorter wavelengths, such as 250-350 nm. At these wavelengths proteins, as opposed to water molecules, absorb the radiation. These systems, however, are less suitable for general types of surgical operations since they are more complicated to operate. Use of such systems has not become standard in most medical facilities and their cost is generally too high to justify their purchase for occasional use in fairly specialized procedures.
The construction of optical fibers used in surgical procedures is fairly simple. A quartz, plastic or silicone cladding is used to constrain the laser light to the quartz core. Theoretically, only a few of the entering photons are directed straight down the axis of the fiber. Transmission of the radiant beam is possible since the rest of the photons are constrained to the core of the fiber due to internal reflectance by the quartz cladding interface. Very few photons escape the fiber. The technology related to the use of silica core fibers in medical lasers is well known, e.g. B. P. McCann, Photonics Spectra, May 1990, pp 127-136.
Differences between these types of optical fibers and those used in telecommunications and data transmission are important. Several design factors must be considered such as sterilizability, quartz core integrity and purity, power capacity and index of refraction of materials of construction.
Generally, 10 to 100 watts of energy are used to perform soft tissue surgery. A fiber optic laser scalpel used externally might be operated much differently than one used in internal or endoscopic surgery. Some endoscopes have multiple channels to accommodate a viewing port or camera, a laser delivery device, and an irrigation supply and accompanying vacuum channel.
Delivery of high power radiation can have a very damaging effect on the fiber tip itself. One of the problems with existing designs is that the tip which directs the laser beam to a right angle becomes overheated. This is caused by an absorption of power (heat) at the reflecting surface. Overheating at or near the surface of the fiber tip can be caused by an accumulation of incompletely burned tissue which rapidly heats up and triggers a process known as thermal runaway. As heat builds up, the fiber tip gets hot and sometimes stats to melt or deform. Often, angle firing fiber optic surgical devices will need to be replaced partway through the surgical operation due to this problem.
Thus, the problems associated with currently available angle delivery fiber optic laser devices are mainly related to fiber overheating and failure. One solution would be to provide a transparent, hard, heat resistant cap over a highly reflective surface in the scalpel tip for deflecting the beam, the cap thus protecting the tip and being highly durable and resistant to thermal damage.
This invention discloses a device wherein the end of the optical fiber is bias cut and, optionally, polished. The tip of the fiber can be placed adjacent to or in intimate contact with a highly reflective mirrored surface. This surface would most likely be a metallic or other reflective material as an insert in the tip assembly or as a layer applied to the tip of the fiber. Depending on the application and operational parameters the instrument is designed around, it may be advantageous to bury the bias cut tip of the optical fiber into the reflective mirrored surface of the reflective cap or insert. Thus, the supplied laser radiation is reflected to the side and leakage of light near the interface between the fiber and the reflective surface is reduced or eliminated. Another embodiment of this invention provides the firing tip with a void or pocket of air at the end of a bias cut fiber. A protective cap made of some material transparent to the laser radiation is applied over the reflective tip or tip assembly to protect the tip from fouling or debris and also to provide a highly durable device at high temperatures and duty cycle.
An embodiment which has proven to be very effective is a truncated ball tip fiber having a bias cut through the ball portion providing a cut surface with a greater surface area than that of the fiber alone. When the tip is cut at an operative angle and polished, a laser beam is reflected internally to the side. The polished end surface can be placed in intimate contact with an efficient reflector such as a mirrored surface having a layer of gold or silver or other metal or material. The result would be to reflect any part of the laser beam which passed through the cut end surface and was not internally reflected. Additionally, the cut surface of the ball tip can be recessed or buried slightly in the reflective surface resulting in a device which transmits the laser beam in a defined angle without overheating or failing.
Another embodiment might have a reflective layer deposited directly onto the cut surface of the fiber. One material capable of being deposited in a very thin coating and producing a very high reflectance is gold. A protective layer over the reflective material could also be applied and be useful to add durability and thermal resistance to the reflective material. U.S. Pat. No. 4,992,087, incorporated herein by reference, discloses a reflective coating consisting of a metal or metal alloy and a process for applying it to a glass surface.
Multiple layer optical interference films, also known as interference filters or films, are well known in the art. Such films comprise alternating layers of two or more materials, typically one with a relatively high index of refraction and the other with a relatively low index of refraction. These materials are also known as dielectrics. Such are well known in the art and can be designed to reflect or transmit light radiation from various portions of the electromagnetic spectrum. Often, materials with high and low indices of refractivity are applied in alternating layers so as to comprise a "quarter wave stack", each layer having an optical thickness equal to approximately one quarter wavelength of the incident light wave. These types of reflectors have been described providing optical absorption losses of as little as 0.0001% to 0.0002%.
Methods for manufacturing these films are described in the prior art. U.S. Pat. No. 4,925,259, incorporated herein by reference, describes a damage-resistant dielectric coating formed over a silica substrate. Using a pulsed-plasma assisted chemical vapor deposition process several hundreds and even thousands of layer pairs can be deposited rapidly. Larger differences between the indices of refraction require a lesser number of layer pairs to obtain a given value of reflectance. In some cases, the indices of refractivity of alternating materials can be very similar and the number of layers very great. These coatings seem to have superior damage-resistance to optical radiation, approaching the damage resistance of pure silica. For laser applications using high power, components can be made to withstand high energy flux densities. They are also resistant to abrasion. Since the materials are very similar in composition there are fewer problems associated with differences in thermal and mechanical properties. Peeling and scaling is avoided as are microcracks which, in a given layer, could otherwise occlude the film.
Clinical applications for this invention include surgical ablation, vaporization, incision, excision, coagulation and cauterization of tissue. These operations can be performed in air or in fluid, either in open or in endoscopic methods, through natural body channels or through artificial incisions. Other applications include scientific industrial, entertainment, communications, and other commercial applications where angle delivery of laser beams via optical fibers at any wavelength is useful.